1. Field of the Invention
The invention relates to a thermally-assisted magnetic recording method in which near-field light is applied to a magnetic recording medium to lower a coercivity thereof so as to record information.
2. Description of Related Art
In the past, a magnetic disk unit has been used for writing and reading magnetic information (hereinafter, simply referred to as information). The magnetic disk unit includes, in the housing thereof for example, a magnetic disk in which information is stored, and a magnetic read write head that records information into the magnetic disk and reproduces information stored in the magnetic disk. The magnetic disk is supported by a rotary shaft of a spindle motor, which is fixed to the housing, and rotates around the rotary shaft. On the other hand, the magnetic read write head is formed on a side surface of a magnetic head slider provided on one end of a suspension, and includes a magnetic write element and a magnetic read element that have an air bearing surface (ABS) facing the magnetic disk. In particular, as the magnetic read element, a magnetoresistive (MR) element exhibiting MR effect is generally used. The other end of the suspension is attached to an end of an arm pivotally supported by a fixed shaft installed upright in the housing.
When the magnetic disk unit is not operated, namely, when the magnetic disk does not rotate and remains stationary, the magnetic read write head is not located over the magnetic disk and is pulled off to the outside (unload state). When the magnetic disk unit is driven and the magnetic disk starts to rotate, the magnetic read write head is changed to a state where the magnetic read write head is moved to a predetermined position over the magnetic disk together with the suspension (load state). When the rotation number of the magnetic disk reaches a predetermined number, the magnetic head slider is stabilized in a state of slightly floating over the surface of the magnetic disk due to the balance of positive pressure and negative pressure, and thus, information is accurately recorded and reproduced.
In recent years, along with a progress in higher recording density (higher capacity) of the magnetic disk, improvement in performance of the magnetic read write head and the magnetic disk has been demanded. The magnetic disk is a discontinuous medium including collected magnetic microparticles, and each magnetic microparticle has a single-domain structure. In the magnetic disk, one recording bit is configured of a plurality of magnetic microparticles. Since it is necessary for the asperity of a boundary between adjacent recording bits to be small in order to increase the recording density, it is necessary for the magnetic microparticles to be made small. However, if the magnetic microparticles are made small in size, thermal stability of the magnetization of the magnetic microparticles is disadvantageously lowered with decrease in volume of the magnetic microparticles. To solve the issue, increasing anisotropy energy of the magnetic microparticle is effective. However, increasing the anisotropy energy of the magnetic microparticle leads to increase in coercivity of the magnetic disk, and as a result, difficulty occurs in the information recording in the existing magnetic head.
As a method to solve the above-described difficulty, a so-called thermally-assisted magnetic recording has been proposed. In the method, a magnetic disk with large coercivity is used, and when information is written, heat is applied together with the magnetic field to a section of the magnetic disk where the information is to be written to increase the temperature and to lower the coercivity of that section, thereby writing the information. Hereinafter, the magnetic head used in the thermally-assisted magnetic recording is referred to as a thermally-assisted magnetic recording head.
In performing the thermally-assisted magnetic recording, near-field light is generally used for applying heat to a magnetic disk. For example, in Japanese Unexamined Patent Application Publication No. 2001-255254 and in Japanese Patent No. 4032689, disclosed is a technology of allowing frequency of light to coincide with a resonant frequency of plasmons that are generated in a metal, by directly applying the light to a plasmon generator, in order to generate near-field light. In the method of directly applying light to a plasmon generator, however, the plasmon generator itself overheats and accordingly deforms, depending on usage environment or conditions. Therefore, practical realization of the method is difficult.
Therefore, as a technology capable of avoiding such overheating, in Japanese Patent No. 4104584, a thermally-assisted head using surface plasmon polariton coupling is proposed. In this technology, without direct irradiation of light propagating through a waveguide (guided light) to a plasmon generator, the guided light is coupled to the plasmon generator through evanescent coupling, and surface plasmon polaritons generated on a surface of the plasmon generator are used.
In the thermally-assisted magnetic recording head using such surface plasmon polaritons, temperature increase of the plasmon generator is suppressed to some extent. However, it was confirmed that, when such a high temperature state is continued over a long period of time, deformation (expansion and shrinkage) due to heat may occur in a section, where a volume is low and where the heat particularly concentrats, of the plasmon generator in the vicinity of the air-bearing surface.